I. Field of the Invention
This invention relates generally liquid medicament, and more particularly to a single-use, low-cost, disposable nozzle assembly for a spring forward injector module.
II. Discussion of the Prior Art
Various forms of needleless hypodermic drug injection devices are known in the art. The Scherer U.S. Pat. No. 2,754,818 discloses one such device in which a disposable ampule filled with a predetermined dose of a wet medicine is loaded into a chamber proximate an ejection orifice in a permanent nozzle assembly. A powerful spring is cooperatively associated with a plunger and when the spring force is released, the plunger is driven to discharge the contents of the ampule through the orifice in a permanent nozzle.
The Gordon U.S. Pat. No. 3,330,276 describes another hypodermic jet injector device having the ability to draw a predetermined dosage of a liquid medicament from a supply vial, through a ball-valve arrangement into a cylinder containing a spring-loaded piston. When the spring energy is released, the piston is driven forward to force the liquid, under high pressure, out through the ejection orifice in a permanent nozzle.
The Dunlap U.S. Pat. No. 4,507,113, assigned to Derata Corporation of Minneapolis, Minn., (applicant's assignee), discloses a method and apparatus for filling the internal cylinder of a spring-powered jet injector from a supply vial directly through the ejection orifice, thereby obviating the need for a complex valve system. This results in essentially zero residual drug retention in the jet injection apparatus following the triggering thereof.
The above-identified patents each contemplates a device which includes a nozzle assembly forming a permanent part of the jet injector body. With the concern over the spread of AIDS, hepatitis and other viral diseases, medical practitioners have become quite concerned over the possibility of accidental "sticks" when drawing blood from a patient or when disposing of the conventional hypodermic needles in waste containers and the like. Thus, it is desirable to be able to administer drugs hypodermically, but without utilizing skin-penetrating needles.
The Lindmayer et al. U.S. Pat. No. 4,518,385 describes a needleless hypodermic injector incorporating a disposable syringe which comprises a tubular plastic barrel which includes an ejection orifice formed in a gem insert fitted into the tubular barrel. It further includes a plastic plunger slidably disposed in the barrel. Because the barrel is not designed to withstand the relatively high hydraulic pressures in encountered during the administration of a needleless injection, it is necessary in the Lindmayer design to provide a reusable head having the gem insert with the injection orifice embedded in the head. Because of the cost involved, the head is intended to be reusable for a series of injections and, thus, cannot be used in a clinic situation where drugs are to be administered to different patients. Moreover, in filling the barrel from a medicament vial, a needle is utilized to puncture the elastomeric seal on the vial cap. The current trend has been to eliminate needles of all types for the reasons already indicated.
In the case of the prior art needleless injectors heretofore described, during the administration of an injection, the fluid jet driven at high pressure through the patient's skin may result in some minor amount of bleeding and because the nozzle assembly of the jet injector is pressed firmly against the skin at the moment of release and for a short time thereafter, there is a possibility that blood might flow back into the ejection orifice to contaminate the nozzle. As such, to avoid cross-contamination of blood between different patient's being treated in a hospital or clinic situation, it would heretofore be necessary to disassemble the drug injector and sterilize those portions of the assembly that could conceivably retain contaminated blood.